a. Technical Field
The present invention relates to hearing devices, and, more particularly, to hearing devices that are semi-permanently positioned in the ear canal for improved energy efficiency, sound fidelity, and inconspicuous wear.
b. Description of the Prior Art
(1) Brief Description of Ear Canal Anatomy and Physiology
The external acoustic meatus (ear canal) is generally narrow and tortuous as shown in the coronal view in FIG. 1. The ear canal 10 is approximately 23-29 millimeters (mm) long from the canal aperture 17 to the tympanic membrane 18 (eardrum). The lateral part, a cartilaginous region 11, is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region 11 of the ear canal 10 deforms and moves in response to the mandibular (jaw) motions, which occur during talking, yawning, eating, etc. Hair 12 is primarily present in the cartilaginous region. The medial part, a bony region 13 proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin 14 in the bony region 13 is thin (relative to the skin 16 in the cartilaginous region) and is sensitive to touch or pressure. A characteristic bend 15 roughly occurring at the bony-cartilaginous junction 19 separates the cartilaginous and bony regions 11 and 13, respectively. The magnitude of this bend varies significantly among individuals.
A cross-sectional view of the typical ear canal 10 (FIG. 2) reveals generally an oval shape with a long diameter DL in the vertical axis and a short diameter DS in the horizontal axis. Canal dimensions vary significantly among individuals as shown below in the section titled Experiment-A. The long/short ratio (DL/DS) ranges from 1:1 to 2:1. The diameter ranges from as little as 4 mm (DS in the bony region 13 in small canals) to as much as 12 mm (DL in the cartilaginous region 11 in large canals).
Physiological debris 4 in the ear canal is primarily produced in the cartilaginous region 11, and includes cerumen (earwax), sweat, and oils produced by the various glands underneath the skin in the lateral portion of the cartilaginous region. Cerumen is naturally extruded from the ear canal by the process of lateral epithelial cell migration (see, e.g., Ballachanda, The Human Ear Canal, Singular Publishing, 1950, pp. 195). There is no cerumen production or hair 12 in the bony part of the ear canal. The ear canal 10 terminates medially with the tympanic membrane 18. Externally and lateral to the ear canal are the concha cavity 2 and the auricle 3.
Several types of hearing losses affect millions of individuals. Hearing loss naturally occurs beginning at higher frequencies (4000 Hz and above) and increasingly spreads to lower frequencies with age.
(2) The Limitations of Conventional Canal Hearing Devices
Conventional hearing devices that fit in the ear of individuals generally fall into one of 4 categories as classified by the hearing aid industry: (1) the Behind-The-Ear (BTE) type which, as the designation indicates, is worn behind the ear and is attached to an ear mold which fit mostly in the concha; (2) the In-The-Ear (ITE) type which fits largely in the auricle and concha areas, extending minimally into the ear canal; (3) the In-The-canal (ITC) type which fits largely in the concha area and extends into the ear canal (see, e.g., Valente M., Strategies for Selecting and Verifying Hearing Aid Fittings, Thieme Medical Publishing, pp. 255-256, 1994), and (4) the Completely-In-the-Canal (CIC) type which fits completely within the ear canal past the aperture (see, e.g., Chasin, M. CIC Handbook, Singular Publishing, 1997 (referred to hereinafter as “Chasin”), p. 5).
The continuous trend for the miniaturization of hearing aids is fueled by the demand for invisible hearing products in order to alleviate the social stigma associating hearing loss with aging and disability. In addition to the cosmetic advantage of a CIC device 20 (FIG. 3), there are actual acoustic benefits resulting from the deep placement of the device within the ear canal. These benefits include improved high frequency response, less distortion, reduction of feedback and improved telephone use (e.g., Chasin, pp. 10-11).
However, even with these significant advances leading to the advent of CIC technology, there remain a number of fundamental limitations associated with the underlying design and configurations of conventional CIC technology. They include: (a) frequency device handling, (b) acoustic feedback, (c) custom manufacturing & impression taking, (d) limited energy efficiency, (e) size limitation due to space inefficiency of enclosure, and (f) occlusion related problems. These limitations are discussed in more detail below.
(a) Frequent device handling:
Conventional CIC devices require frequent insertion and removal from the ear canal. Manufacturers often recommend daily removal for cleaning and maintenance of the CIC device (see, e.g., Users's Instructions, SENSO CIC and Mini Canal, Widex Hearing Aid Co. February 97, pp. 11, 16; and General Information for Hearing aid Users, Siemens Hearing Instruments, Inc. March 98, p. 8). Frequent removal of conventional CICs is also required for relieving the ear from the pressures of the device occluding the cartilaginous region. Furthermore, CIC hearing aid removal is also required in order to replace its battery, typically lasting from 1 to 2 weeks. The manual dexterity required to handle a CIC hearing device frequently poses a serious challenge to the many hearing impaired persons represented by the elderly. These individuals typically suffer from arthritis, tremors, or other neurologic problems that limit their ability to handle a miniature hearing aid.
(b) Acoustic feedback:
Acoustic feedback occurs when a portion of the sound output, typically from a receiver (speaker), leaks to the input of a sound system such as a microphone of a hearing aid. This leakage often causes a sustained oscillation, which is manifested by “whistling” or “squealing”. Feedback is not only annoying to hearing aid users but also interferes with their communication. Feedback is typically alleviated by occluding (sealing) the ear canal tightly, particularly at the cartilaginous region 11, as illustrated with the CIC hearing device in FIG. 3.
(c) Custom manufacturing & impression taking:
Conventional CIC devices are custom made according to an impression taken from the ear of the individual. The device housing 22 (FIG. 3), known as a shell, is custom fabricated according to the impression, to accurately assume the shape of the individual ear canal. Customizing a conventional CIC is required in order to minimize feedback and to improve comfort of wear. But custom manufacturing is time consuming and results in considerable cost overhead for the manufacturer, ultimately reflected in the price of the CIC device to the consumer (user). Furthermore, impression taking is often uncomfortable for the user.
(d) Limited energy efficiency:
The efficiency of a hearing device is generally inversely proportional to the distance or residual volume 25 (FIG. 3) between the receiver (speaker) end 23 and the tympanic membrane 18, the closer the receiver is to the tympanic membrane, the less air mass there is to vibrate, and thus, less energy is required. However, due to concerns related to discomfort and difficulty of insertion, CIC products are typically tapered at their medial end 23 (e.g., Chasin, pp. 9-10) and relatively shallow in their placement in order to avoid substantial contact with the bony portion of the ear canal as shown in FIG. 3.
(e) Size limitation due to space inefficiency of enclosure:
Since a conventional CIC is frequently handled by a wearer, the enclosure 22 (FIG. 3) must be made durably thick in order to protect the components contained within (battery 26, microphone 27, amplifier 28 and receiver 29). Therefore, a shell, or main housing, is typically made of rigid material such as plastic (e.g. acrylic). Typical thickness for this housing or enclosure of CIC devices is 0.5 to 0.7 mm, which adds considerable dimensions to the conventional CIC. Furthermore, conventional shells enclose the battery along with other components, which makes the overall housing large. This space inefficiency renders the device unsuitable for many individuals with small or highly contoured ear canals who would not be able to comfortably tolerate insertion and wear of a CIC device deep in the ear canal.
(f) Occlusion related problems:
(i) Discomfort, irritation and even pain may occur due to canal abrasion caused by frequent insertion and removal of a CIC hearing aid. A removal strand 24 (FIG. 3) is generally provided with CIC devices to assist the wearer in the daily removal process. Due to the resultant discomfort and abrasion, hearing devices are frequently returned to the manufacture for improvement of the custom fit and comfort (e.g., Chasin, p. 44). “The long term effects of the hearing aid are generally known, and consist of atrophy of the skin and a gradual remodeling of the bony canal. Chronic pressure on the skin lining the ear canal causes a thinning of this layer, possibly with some loss of skin appendages” (Chasin, p. 58).
(ii) Moisture produced in the cartilaginous ear canal causes damage to the ear canal and the hearing device therein. “The humidity in the occluded portion of the canal increases rapidly. This is worse during hot and humid weather, following exercise” (Chasin, pp. 57-58). It is often recommended that the CIC device should be removed from the ear canal daily to reduce the damaging effects of moisture in the canal.
(iii) Cerumen impaction (blockage of the ear canal by earwax) may occur when cerumen, produced in the cartilaginous region, is pushed and accumulated deeper in the bony region of ear canal by the frequent insertion of a CIC hearing device (e.g., Chasin, p. 27, pp. 56-57). Cerumen can also build up on the receiver of the hearing device causing frequent malfunction. Cerumen contamination due to frequent insertion is probably the most common factor leading to hearing aid damage and repair (see, e.g., Oliveira, et al, The Wax Problem: Two New Approaches, The Hearing Journal, Vol. 46, No. 8).
(iv) The occlusion effect, a common acoustic problem attributable to occlusion of the ear canal by the hearing device, is manifested by the perception of the user's (wearer's) own voice (“self-voice”) being loud and unnatural compared to that with an open (unoccluded) ear canal. This phenomenon is sometimes referred to as the “barrel effect”, since it resembles the experience of talking into a barrel. The occlusion effect, which may be experienced by plugging the ears with fingers while talking, is generally related to self-voice resonating within the ear canal. For hearing aid users, the occlusion effect is inversely proportional to the residual volume 25 (FIG. 3) of air between the occluding hearing device and the tympanic membrane. Therefore, the occlusion effect is considerably alleviated by deeper placement of the device in the ear canal. Incorporating a vent 21 across the CIC hearing device 20 can also alleviate this effect.
The above limitations in conventional CIC devices are highly interrelated. For example, when a CIC is worn in the ear canal, movements in the cartilaginous region “can lead to slit leaks that lead to feedback, discomfort, the occlusion effect, and ‘pushing’ of the aid from the ear” (Chasin, pp. 12-14). The relationship between the limitations is often adverse. For example, occluding the ear canal tightly is desired on one hand to prevent feedback. On the other hand, however, tight occlusion leads to various adverse side effects as mentioned above. Attempts to alleviate the occlusion effect by a vent 21 provide an opportunistic pathway for leakage and feedback. For this reason, the vent 21 diameter is typically limited in CIC devices to 0.6-0.8 mm (e.g., Chasin, pp. 27-28).
(3) Review of state-of-the-art in related hearing device technology
Ahlberg et al and Oliviera et al in U.S. Pat. Nos. (USPNs) 4,880,076 and 5,002,151 respectively, disclose a compressible polymeric foam assembly attached to an earpiece of a hearing device. The compressible foam assembly (FIG. 1 of both Ahlberg and Oliviera) is inserted in to the ear canal to couple sound and seal acoustically therein. The foam seal is attached serially to the earpiece, which adds a considerable dimension to overall length of the hearing device. Therefore, the application of such compressible foam assembly is limited to BTE and ITE devices which have housings positioned external to the ear canal.
Cirillo in U.S. Pat. No. 4,830,139 discloses means for holding a speaker mold (16 in Cirillo's FIG. 1) in the ear canal via a sealant made of flexible gelatinous water-soluble material. The mold is attached to a wire (18) extending to the outside of the ear canal, and therefore, Cirillo's proposal is presumably also for hearing devices that are positioned outside the ear canal. It does not deal with devices that are completely positioned in the ear canal. Furthermore, since the sealant is water-soluble, it can also be assumed to be suitable only for short-term use as it will deteriorate with moisture exposure (e.g., as will occur when the wearer is taking a shower or is caught in the rain).
Sauer et al in U.S. Pat. No. 5,654,530 disclose an insert associated with an ITE device (Sauer's FIG. 1) or a BTE device (Sauer's FIG. 2). The insert is stated to be a “sealing and mounting element” made of “soft elastic material having slotted outer circumference divided into a plurality of fan-like circumferential segments”. The sealing element is positioned at the lateral portion of the ear canal as shown in Sauer's figures. According to the patent, the insert is for ITEs and BTEs only, not for inconspicuous hearing devices that are deeply and completely inserted in the ear canal. The insert as disclosed is used in the cartilaginous area, thus occluding the ear canal in the region of hair, cerumen and sweat production. Clearly, long term use (without daily removal) will interfere in the natural production of physiologic debris.
Garcia et al. in U.S. Pat. No. 5,742,692 disclose a hearing device (10 in Garcia's FIG. 1) attached to a flexible seal 30 which is fitted in the bony region of the ear canal. The device 10 comprises hearing aid components (i.e., microphone 12, receiver 15 and battery 16, etc., as shown by Garcia) which are contained within a single “unitary” housing 20. The device 10 is not likely to fit deeply and comfortably in many small and contoured canals due to the space inefficiency associated with the unitary housing 20. In addition to the size disadvantage, the device 10 occludes the ear canal in the cartilaginous region as shown in Garcia's FIG. 2.
Henneberger and Biermans in U.S. Pat. Nos. 4,680,799 and 4,937,876, respectively, also disclose hearing aids with conventional housings, which occlude the ear canal and comprise a unitary enclosure for microphone, battery and receiver components therein.
Weiss et al. in U.S. Pat. Nos. 3,783,201 and 3,865,998 disclose an alternate hearing device configuration which fits partially in the ear canal (FIG. 1 in both the Weiss '201 and '998 patents) with a separate microphone 14 and receiver 18. The main housing, enclosing battery and amplifier, is designed to fit in the concha area outside the ear canal as shown. The microphone 14 is positioned in the pinna completely outside the ear canal. The device is clearly visible to the casual observer.
Geib in U.S. Pat. No. 3,527,901 discloses a hearing device with housing made of soft resilient material, which encloses the entire body of the device. This approach eliminates conventional rigid enclosures, and is presumably more comfortable to wear. However, the unitary flexible enclosure provides no improvement in space efficiency and also poses serious concerns regarding the reliability of interconnects, and of the device in general, during frequent handling. The disclosed hearing device was not designed to fit entirely in the ear canal, Geib stating that “the hearing aid makes a much better fit within the concha and ear canal of the user thereby providing a more effective seal and reducing the problems of direct acoustic feedback” (col 2, lines 40-43).
Hardt in U.S. Pat. No. 4,607,720 discloses a hearing device which is mass-producible with a soft sealing plug that is serially attached to the receiver. Although the problem of custom manufacturing is addressed, the unitary enclosure (containing major hearing aid components; battery, microphone and receiver) is, as with other prior art proposals, space-inefficient for deep canal fittings.
Voroba et al in U.S. Pat. No. 4,870,688 also disclose a mass-producible hearing aid, which includes a solid shell core (20 in Veroba's FIGS. 1 and 2) with a flexible covering 30 affixed to its exterior. Similarly, the rigid core represents a unitary enclosure for all major hearing aid components, and thus, is space-inefficient for deep canal fittings.
Hartl et al. in U.S. Pat. No. 4,639,556 disclose a hearing aid with a flexible printed circuit board attached to a face-plate. The flexible circuit board and major hearing aid components are also enclosed in a unitary housing (1 in Hartl's FIG. 1). Similarly, this leads to a space-inefficient design for deep canal fittings.
McCarrel et al, Martin, Geib et al, and Adelman, in U.S. Pat. Nos. 3,061,689, RE 26,258, 3,414,685 and 5,390,254, respectively, disclose miniature hearing devices with a receiver portion flexibly separate from a main part. The receiver portion insertable into the ear canal with the main part occupying the concha (McCarrel's FIG. 2, Geib's FIG. 10, and Adelman's FIG. 3B). This placement facilitates access to the device for insertion and removal. In each of these disclosures, the aforementioned main part contains all the major components of the hearing device, including among others the battery, amplifier and microphone, except the receiver. Therefore, this main part is not sufficiently space-efficient to fit past the aperture of the ear canal for most individuals.
Shennib et al in U.S. Pat. No. 5,701,348 disclose an articulated hearing device with flexibly connecting modules, stating that “the main module 12 includes all of the typical components found in hearing devices, except for the receiver” (col. 6, lines 64-66). The main module includes a battery 16, a battery compartment 15, circuit 17 (amplifier) and microphone 14. Because if its articulated design and assorted soft acoustic seal 43, the hearing device disclosed by Shennib is suitable to fit a variety of ear canals without resorting to custom manufacturing, and thus can be mass-producible as disclosed. Although a CIC configuration is disclosed (see Shennib's FIG. 23), the depth of insertion, particularly for small and contoured ear canals, is severely limited by the design of the main module 12 which contains the power source (battery) along with other major components (e.g., the microphone). Furthermore, in each of its disclosed configurations, the device substantially occludes the ear canal in the cartilaginous region, which would interfere with hair and the natural production of physiologic debris. In addition, the disclosed CIC configuration is designed for insertion and removal by a wearer with good dexterity (col. 11, lines 18-20). Therefore, the disclosed CIC device would be unsuitable for continuous long-term use in the ear canal, particularly for persons lacking such dexterity.
It is the principal objective of the present invention to provide a highly space-efficient hearing device, which is suitable to be completely positioned in the ear canal.
Another objective is to provide a design for a hearing device which is mass-producible, and which requires neither custom manufacture nor the taking of individual ear canal impressions.
A further objective of the invention is to provide a hearing device which occludingly seals the ear canal in the bony region, but not at the cartilaginous region, and thus does not interfere with hair and the natural production and elimination of physiologic debris in the ear canal.
Yet another objective is to provide a semi-permanent hearing device which is inserted by a physician, or by other professionals under the supervision of a physician, for long-term use in the ear canal.
Semi-permanent, or alternatively long-term use, is defined herein as continuous placement and use of the hearing device within the ear canal without any removal, daily or otherwise, for at least a month.